Technique 7 of 8 · Recognising patterns
Understand the 1–2–2–1 pattern
The guide and all minesweeper techniques
Minesweeper techniques
- 1Finding certain minesStart here
- 2Finding safe cellsStart here
- 3Flagging and chordingCore technique
- 4Comparing neighbouring numbersShared cells
- 5Subtracting known minesSimplifying clues
- 6The 1–2–1 patternRecognising patterns
- 7The 1–2–2–1 patternRecognising patterns
- 8Using the remaining mine countFinishing a board
The standard 1–2–2–1 arrangement has four covered cells along one side of four clues. The middle two covered cells contain mines; the outer two are safe.
Check the groups carefully. The left 1 counts the first pair, the first 2 counts the first three cells, the second 2 counts the last three, and the right 1 counts the last pair.
Example 1: The two extra mines are in the middle
Step 1 of 3
The left pair supplies one mine to the first 2. The third cell must supply its second.
Subtract the left 1's pair from the first 2's group. The third covered cell must be a mine. Comparing from the right proves the second covered cell is a mine.
Those middle mines satisfy both end 1s, so the outer covered cells are safe. Every conclusion agrees with both 2s.
Work inside the solid frame. Every possible mine neighbour of these clues is inside it. Cells beyond the frame are background, not revealed zeros or extra clues.
Flags are proved mines. A tick marks a cell proved safe; its number is not shown.
Blue-ringed numbers are the clues to compare. Shading marks the cells being discussed.
Try it yourself
Try the reasoning yourself. Choose an answer to see the explanation.
This is the same arrangement running down the board. Prove its mines, then its safe cells.
Practice only: no clock, saved game or hint charge.
Task 1 of 2: Flag both certain mines.
Choose a cell on the board.
Work inside the solid frame. Every possible mine neighbour of these clues is inside it. Cells beyond the frame are background, not revealed zeros or extra clues.
Practice close-up: rows 1–4, columns 1–4.
Flags are proved mines. A tick marks a cell proved safe; its number is not shown.
How to spot it faster
- Start at an end 1 and compare it with the adjacent 2.
- Repeat from the other end rather than assuming symmetry from appearance.
- Check all four conclusions against the displayed clues.
Common mistakes
Remembering the answer to 1–2–1 instead
In the three-cell pattern the mines are at the ends. In this four-cell arrangement they are in the middle. Derive them from the clue groups when unsure.
Ignoring a covered cell behind the clues
An extra possible mine can change the groups. The standard answer only applies when the remaining covered neighbourhood matches.
Questions
Further reading
Try it
Find four neighbouring clues along an opening. Compare from each end and verify the remaining groups before using the pattern.
Play solo Minesweeper